Cherokee 96 said:
...One portion of our plant(section A) which has controllogix and couple of HMI's has a different 3rd octet in comparison with the rest of the plant. I think all of these communicate with each other.
But how do I connect with this Section A. Do I change my IP address everytime when I have to connect to Section A.
..
The answer to your question best lies in you learning how "they" communicate with each other. If by "they" you mean the different sections of your plant.
If there are interconnecting appliances, such as switches/routers, between each section of the plant, then there is most likely a preconfigured Industrial Automation and Control System (IACS) architecture. This involves segmenting the sections of the plant in a physical/logical manner which places each section on a defined but unique subnet, while still allowing them to communicate with each other, even though they are assigned different subnets.
Each of these segmented subnets, in an IACS, are known as a Virtual Local Area Network, or VLAN. These are configured and propogated on the switch/router appliances and their specific configuration will determine which nodes, on the different VLANs, will be able to communicate, or route data between each other. This, in an IACS, is reffered to as Inter-VLAN Routing. A typical setup will define the third octet as the VLAN number and the fourth octet as the node number. Because the appliances handle the routing, using gateway addressing, there is no need to ensure that individual nodes are configured with the same subnet address. Likewise, computer workstations may not need to be reassigned with different IP addresses, or use a more open subnet to achieve a farther reach.
Example:
VLAN 50 / Node 100
IP: 10.5.50.100
Subnet: 255.255.255.0
Gateway: 10.5.50.1
VLAN 55 / Node 100
IP: 10.5.55.100
Subnet: 255.255.255.0
Gateway: 10.5.55.1
VLAN 50 may be configured to Inter-VLAN Route to VLAN 55. If you are on say VLAN 50 using Node address 200 then all of the Nodes on VLAN 50 and 55 will be exposed to your workstation. All while the workstation's subnet remains at 255.255.255.0.
If this is how your plant network is designed then you are looking at different VLANs when you view the different third octets in the IP addressing schema for the different sections of the plant.
Where you connect into the IACS will determine what configuration your workstation will need to use. If a specific port on a network appliance is preassigned for this task then it may even be automatic. Even if you have to manually assign the configuration, it is possible that Inter-VLAN Routing will expose all sections of the plant to your workstation.
All of that is intended as a part explanation as to how your plant's network may be designed. Until you determine what networking appliances, if any, are interconnecting the sections then the above may only prove academic. You may just have a very basic setup with none of the above and you do need to keep reconfiguring your workstation's IP address or open its subnet up.
One of the commonest misconceptions I see regarding Industrial Ethernet implementations is the assumption that the usage of subnetting in an Office or Commercial setting is the same as its usage in an IACS. This can be far from the case. If your plant does not have an IACS, and standard networking has been applied, then that is a whole other level of misconception.
So...
Cherokee 96 said:
Is there a reason whoever commissioned this did this way ?...
Depending on whether you have a well designed IACS, or not; they did it that way because they were following good practices, or, they applied their basic Ethernet knowledge and thought they were following good practices.
Regards,
George
